This invention relates to a method of machining, and particularly to a method of machining suitable for high temperature nickel based metal alloys including the type known in the art as superalloys, as well as other difficult-to-work alloys based on iron and cobalt.
The high temperature nickel based superalloys, for example Inconel.RTM. alloys (available from Huntington Alloys, Inc., Huntington, W.Va.), present the advantages of deformation resistance and retention of high strength over a broad range of temperatures. Because of their high strength at elevated temperatures, however, these alloys are much more difficult to machine than steels.
Ceramic-metal (cermet) tools, which have greatly improved the productivity and efficiency of the metal removal process in steel machining, for the most part have not proven effective in machining of nickel based alloys. These cermet materials are based principally on refractory metal carbides or nitrides bonded with cobalt, nickel, molybdenum, or alloy binders. Commercially available cutting tools, for example cobalt cemented tungsten carbide, can be utilized for such machining only at relatively low cutting speeds and hence low productivity.
Attempts have been made to utilize alumina ceramics and alumina-based composites such as alumina-titanium carbide composites for use as cutting tools for high temperature nickel based superalloy machining. The use of this class of materials, however, has been restricted by their inherently low fracture toughness, limiting the usable feed rate and depth of cut. Alumina-silicon carbide whisker composites have provided some increase in fracture toughness, but the whisker component requires careful handling to assure safety and complete homogeneity in fabrication of the material.
Accordingly, it would be of great value to find a method suitable for machining difficult-to-work metals such as high temperature nickel based superalloys using a cutting tool which exhibits improved chemical wear resistance and performance when compared to conventional ceramic metal-cutting tool materials, improved fracture toughness compared to known alumina-titanium carbide composites, and improved ease of fabrication compared to alumina-silicon carbide whisker composite materials. The new and improved method described herein utilizes such a cutting tool.